This invention relates to a magnetic resonance (MR) scanner apparatus. More specifically, this invention relates to a cradle drive and release mechanism for use with an MR scanner to retrievably position a patient cradle in the bore of a magnet and for returning the cradle to a home position on top of a patient transport table.
The magnetic resonance phenomenon has been utilized in the past in high resolution MR spectroscopy instruments by structural chemists to analyze the structure of chemical compositions. More recently, MR has been developed as a medical diagnostic modality having application in imaging the anatomy, as well as in performing in vivo, non-invasive spectroscopic analysis. As is now well known, the MR resonance phenomenon can be excited within a sample object, such as a human patient, positioned in a homogeneous polarizing magnetic field, by irradiating the object with radio frequency (RF) energy at the Larmor frequency. In medical diagnostic applications, this is typically accomplished by positioning the patient to be examined in the field of an RF coil having a cylindrical geometry, and energizing the RF coil with an RF power amplifier. Upon cessation of the RF excitation, the same or a different RF coil is used to detect the MR signals emanating from the patient volume lying within the field of the RF coil. The MR signal is usually observed in the presence of linear magnetic field gradients used to encode spatial information into the signal. In the course of a complete MR scan, a plurality of MR signals are typically observed. The signals are used to derive MR imaging or spectroscopic information about the object studied.
A whole-body MR scanner used as a medical diagnostic device includes a magnet, frequently of solenodial design, to produce the polarizing magnetic field. The bore of the magnet is made sufficiently large to accommodate RF, gradient, and shim coil assemblies, as well as the torso of a patient to be examined. The scanner also includes a table which supports a cradle used to retrievably position a patient within the bore of the magnet. The table is aligned longitudinally with the bore of the magnet and disposed at the same height to facilitate advancement of the cradle between a home position when the cradle is on the table and an advanced position when the cradle is in the magnet. Advancement of the cradle between the advanced and home position is accomplished using a cradle drive system located near the magnet.
The cradle drive system in an MR diagnostic system must be comprised of materials which are non-magnetic, non-conductive, non-hydroscopic, and non-MR active to avoid interference with the imaging process. The cradle drive system needs to be capable of power driven as well as manual operation. Manual operation is useful for either emergency removal of the patient or for aligning the patient prior to scanning. The maximum force that the cradle drive can exert when power driven should not exceed a predetermined adjustable limit of, for example, 30 pounds. This requirement ensures that the cradle drive is effectively disengaged in the event travel in either direction is obstructed. This feature is also useful in the event it is desired to manually override the power drive. The cradle drive system must also be capable of easily engaging and disengaging the patient cradle.
It is, therefore, a principal object of the invention to provide a cradle drive system having the above-noted features.